This invention relates generally to combined refrigerator/freezer appliances.
Combined refrigerator/freezer appliances typically have two or more compartments that are refrigerated to differing temperatures, one being chilled to a temperature well below the freezing temperature of water, such as around 0° F. and the other being chilled to a below ambient temperature, which is above freezing, such as around 40° F. To chill the two different compartments to these temperatures, a refrigeration system is typically employed which includes one or two evaporator components.
In a single evaporator system, such as that disclosed in U.S. Pat. No. 5,490,395, the evaporator is located in, or in close communication with the freezer compartment, and the evaporator is chilled to below the desired temperature for the freezer compartment. Air is circulated over the evaporator to chill the freezer compartment. To cool the refrigerator or fresh food compartment, air is ducted out of the freezer compartment and is circulated through the fresh food compartment, and then returned to the freezer compartment. A separate fan is usually provided for the fresh food compartment air circulation system along with baffles for permitting or preventing the flow of sub-freezing air into the fresh food compartment. Problems that result from single evaporator systems are that the significantly higher humidity levels in the fresh food compartment are transferred to the freezer compartment as the air is circulated between the two compartments, reducing the desired humidity level in the fresh food compartment and increasing a build-up of frost in the freezer compartment, and food odors are also transmitted between the two compartments.
In a dual or multi-evaporator refrigerator/freezer appliance, such as disclosed in U.S. Pat. No. 5,465,591, a separate evaporator is used for each compartment, which addresses some of the problems listed above since the air in each compartment is isolated from the air in other compartments, however, there are significant increased costs for two separate evaporators and possibly two complete refrigeration systems. Also, there are more joints in the cooling system that may fail over time, and the addition of another evaporator and refrigerant system for that evaporator, results in a loss of at least 0.3 to 0.5 cubic feet from the food storage space in the compartments. Also, proving two evaporators results in increased tooling costs and factory complexity.
A single evaporator system is disclosed in U.S. Pat. No. 5,375,428 in which the single evaporator is positioned in the mullion between the freezer compartment and the fresh food compartment. Air is alternately circulated over the evaporator from one of the two compartments, such that the mixing of air between the two compartments is reduced, although not eliminated. This system requires that the evaporator be operated at different pressures, and hence different temperatures, depending on which of the two compartments is being cooled, thereby increasing the complexity of the system and control. Also, in such a system, only one compartment may be cooled at a time, even when both compartments may be demanding cooling.